Fangs evolving from teeth helped snakes spread worldwide

Sydney, Aug 4 (IANS) Fangs which had evolved from early teeth enabled snakes to expand across all continents except Antarctica nearly 60 million years ago, according to a new study. “Understanding the evolution of fangs sheds light on how snakes colonised new environments or adapted to feed on new prey,” said Bryan Fry of the department of biochemistry and molecular biology in Bio21 Institute, University of Melbourne. Fry worked on the study with a team from the Netherlands, US, Israel and Australia.

All snakes with hollow front fangs were believed to descend from a common ancestor but genetic evidence showed that this was not the case. Hollow front fangs instead evolved independently on three separate occasions.

“The true innovation in venom delivery came with the development of hollow-syringe fangs to deliver the venom under high-pressure” added Fry. A major unanswered riddle was how snake species each developed their weaponry.

“The origin and evolution of the snake venom system has long been an area of great controversy and acrimonious debate. It has only become recently evident that venom is a basal characteristic of the advanced snakes.”

All share a common ancestor that had venom glands but used ordinary teeth to chew the venom, and many lineages independently enlarged the rear-teeth.

“Such innovations allowed the snakes to envenomate new prey items, such as being able to efficiently get past the thick fur of mammals or puncture the hard scales of other snakes.”

Among the species of advanced snakes there is a range of front- and rear-fang groups according to whether their fangs face forward (for example cobras and vipers) or face backward (for example grass snakes) in the upper jaw, but it has perplexed snake biologists for years as to whether or not the fangs shared the same evolutionary and developmental origin.

This new evolutionary model reveals that a subset of tooth-forming cells developed independently allowing some teeth to evolve closely with the venom gland into fangs - which have become highly specialised in some species.

The team examined tooth-forming cells in upper jaw of 96 snake embryos by visualising the tooth-forming epithelium (layer of skin cells) in the upper jaw of 96 snake embryos, covering eight species.

They used the sonic hedgehog gene as a marker to three-dimensionally reconstruct the development in 41 of the embryos.